Embodiments of the invention relate to the field of data storage, and in particular, to caching data in a storage cache with flash memory units organized in a RAID configuration.
A cache is a small high-speed memory device interposed between a processor and a larger but slower device, such as main memory or storage. Storage caches temporarily store data that is frequently accessed by host systems from a storage system, which make repeated references to the same data. A cache, during write operations, typically holds write data before it is destaged to primary storage. A cache, during read operations, caches read data after an initial access to data from the storage system's primary storage. Subsequent accesses to the same data will be made to the storage cache. A storage cache allows read data in a storage system to be accessed in a shorter amount of time by a host client system by reducing the number of wait states during data accesses.
Flash memory is a type of non-volatile memory. In particular, flash memory is a type of Electrically Erasable Programmable Read Only Memory (EEPROM) device that can be electrically erased and reprogrammed in blocks. Flash memory has features of the Random Access Memory (RAM) because data is rewritable on flash memory. Flash memory also has features of Read Only Memory (ROM) because flash memory devices are non-volatile. Memory cells are arranged in blocks for erasure and after a block has been erased, the block is available to be reprogrammed. Flash memory has become an increasingly popular form of non-volatile memory because of the flash memory's small size, fast access speeds, shock resistance, and light weight.